In one of my homebrew settings I sort of allow Concentration stacking in that I have consumable magic items called Power Components. A Power Component is consumed in casting a spell, and it allows the caster to choose one method of enhancing the cast spell. One of the enhancements available is to remove the Concentration requirement of the spell. Each Power Component relates to a certain class of spells (Healing, Illusion, Fire, Plant etc.).

This might be a good idea to test the waters with. I can introduce a few consumables to try out the concentration stacking, and see how I feel about it. If I don't like it....well no more of the consumable

Please calibrate your rules for the minmaxed scenario. That's vitally important to game balance.

In other words, let's assume a character with Constitution 20 that is proficient in Constitution ability checks* with at least a bonus of +2 (or 1d4) and the ability to gain advantage on the roll. That character will have a relevant bonus of +12. The probability of making a DC 15 check is thus 99%. (The probability of rolling two d20s and rolling 3 or better on both is exactly 99%)

*) Yes, I am aware this should probably be proficiency in Constitution saves, but since 77IM wrote checks, I'm going with checks for the time being.

At least add the level of the highest levelled spell to your DC.

Example: combining a level 1 spell with a level 3 spell sets the DC at 15+3=18.

I would also clarify that this sets the minimum DC for concentration saves. That is, even if you only take a single point of damage, the Concentration save DC is minimum 15 (or 18, in my example). Failure means you lose both spells of course.

Good luck with your rule.

Thanks for the analysis!

1) I'm not aware of any ability that grants proficiency on Constitution checks; the closest I can see is Remarkable Athlete which grants half-proficiency (+3) and requires substantial investment in Champion fighter. Or, of course, just being a bard with Jack of all Trades (bards already suffer from MAD though). This is why I prefer to use checks instead of saves -- that is a very deliberate choice to avoid the myriad things that pile on save bonuses. Are there other abilities that grant blanket proficiency to Con checks?

2) +1d4 and Advantage usually require a resource expenditure to activate, which I am OK with. There's an edge-case where long-lasting concentration spells can benefit from someone using guidance out of combat (it has to be another character because guidance itself is concentration) but there aren't a super lot of long-lasting concentration spells where this is worthwhile.

3) If a player really optimized their PC to stack concentration, I'm totally OK with that, because it's not that beneficial. Suppose a 17th level lore bard with JoaT and max Con plus a manual of bodily health or whatever has a +9 bonus, and can use bardic inspiration on herself because she has many uses per day, has to roll a 6 or better on 1d20+1d12 to activate a second spell... that's like a 95% chance of success. But what does that really get her? Maybe she can run globe of invulnerability and greater invisibility at the same time? That's pretty cool, but I don't think it's game-breaking at all, considering the opportunity cost of maxing Con.

It doesn't seem like a huge buff to wizards given what seems like a significant hit on number of spells/day.

I'm not sure if that's the best way of doing it, though. Are they any more likely to take that 'nifty' concentration spell knowing they are going to burn through higher level slots just to concentrate on a different spell?

Originally Posted by clearstream

I might try these out in my campaign. To do that, I think my ideal would be to translate this into a caster item, either with charges or that I can easily remove from the campaign.

Fluff-wise, That would work. You need to use the higher level slot to power the item.

Just have more concentration spells follow the model of Bestow Curse (removes concentration requirement when cast 2 slots higher). No keyword needed.

I'd only apply that to lower-level concentration spells, though. Say, no higher than 3rd level, with maybe some very rare exceptions.

This is the correct answer for one looking to bend the concentration rules. We already have the example of Bestow Curse. Maybe other spells will have to have a higher cost before loosing the concentration requirement, but that will have to be tailored for each spell.

This might be a good idea to test the waters with. I can introduce a few consumables to try out the concentration stacking, and see how I feel about it. If I don't like it....well no more of the consumable

It also allows you to control how often concentration stacking is available by controlling the dispensation of the consumables.

Especially for NPCs. The NPC "Archmage" stat block is so pale it isn't even funny. Sure it commands respect - from a single-digit levelled party. In my mind NPCs like Vizeran (Out of the Abyss) or Mordenkainen (Curse of Strahd) needs much more loving attention than that feeble effort. Most critically, the ability to break the limits of concentration and action economy. (The ability to break attunement limits is mainly a concern for characters with many strong items, or player characters in other words).

I was running X2 Castle Amber. One of the creatures is a Brain Collector that, well, collects brains. It's also a spell caster. The encounter is a solo encounter, so it's much easier in 5e. When I converted the monster to 5e I gave it the ability to concentrate on one spell for each brain it had with no chance of failure. (at least, I think it had no chance. Definitely could concentrate on more than one spell at a time).

It was a definite improvement and a shock to the players for the few rounds it was alive.

The spell slot upcasting seems like one way to make this work, but I wonder if the caster might move more quickly toward a 5 minute workday because they blow all their spell slots too quickly. The proposed rule also seems a bit fiddly because of how it looks like it is dependent on order of simple or regular concentration spells. If looking at using upcasting to bypass concentration, I would suggest just requiring the second spell to be cast 2 levels higher and leave it at that. I like the one concentration saving throw at disadvantage.

I think there might be another way to look at this though, which may or may not work depending on where you think the resource burn should be for bypassing concentration. It could be modeled on the extreme effort of the alternate use of the wish spell or a second use of the evocation wizard's Overchannel feature where the caster takes damage. If the caster took 1d4 (or 1d6) psychic damage per spell level for each concentration spell aside from their highest-level one that is active at the end of their turn, it would influence not only whether a caster decided to bypass concentration but also for how long. As an example, if the caster had both a 4th-level and a 2nd-level concentration spell active, they would take 2d4 psychic damage at the end of their turn. If they were concentrating on a 4th-, 2nd-, and 1st-level spell at the end of their turn, they would take 3d4 psychic damage.

Similarly to Overchannel, this damage ignores resistance and immunity. Using hp as the limiting factor would allow them to still use their high-level spell slots for awesome spells. In this scenario, I think I would refrain from having them make the concentration saving throws at disadvantage because they will be making an extra saving throw at the end of their turns from the psychic damage.

This could open up a new sorcerer metamagic option where the sorcerer could spend sorcery points to avoid the damage from multiple concentration spells. One way would be to spend sorcery points equal to twice a spell's level to make it not concentration (which has the additional benefit of not loosing concentration). Another would be to spend 1 sorcery point per spell level when the spell is cast to avoid the concentration damage for that spell at the end of your turns.

I think there are some worthwhile options being discussed. Some people have expressed reservations about making the caster more powerful than non-casters, but the goal should be to offer flexibility, not power. My first 5E character was a Valor Bard, and I can certainly understand the frustration of having successfully cast one Concentration spell, and then having very few non-Cantrip options after that point unless you wanted to drop a spell. Meanwhile, the Evoker Wizard is rocking it out just fine even with a few Concentration spells, while the Illusionist/Enchanter/Transmuter/etc. look on in annoyance.

Maybe one easy rule would be to allow additional Concentration spells, but they immediately default to just a single round in duration since you spent a minimal amount of effort concentrating on them (and being wounded or otherwise interrupted can shorten that per normal)? So, you've successfully cast Bane on 3 enemies, but now you really want to cast Bless just for a round to help your party try to get one crucial hit in or try to Save against one particular spell.